1. Field of the Invention
The present invention relates to a probe for use in an eddy current testing.
2. Description of the Related Art
As a non-destructive testing method for detecting defects in metals, an eddy current testing (ECT) has been known. In the eddy current testing, a magnetic flux generated by an ECT coil to which an excitation current is applied generates an eddy current in a member to be measured, and a detection signal representing the magnetic flux generated by the eddy current is obtained as an output signal of the ECT coil. The detection signal thus obtained represents a position, shape, depth, or the like of a defect (flaw) of the test object. As such, the flaw detection is performed based on the detection signal.
However, in a case where the test object is a magnetic material, or in a case where the test object contains a magnetic material in an area under test, local variations in permeability are caused mainly due to variations in the material and, as a result, noise contained in the detection signal is increased and thereby lowering defect detection precision.
Against the lowered detection precision due to noise caused by variations in permeability, a countermeasure is proposed (for example, Japanese Patent Application Laid-Open No. 2008-309573) in which whether the detection signal is derived from a flaw of the test object or from noise is determined, and another countermeasure is proposed (for example, Japanese Patent Application No. 2005-55325) in which a permanent magnet for magnetic saturation is provided to the ECT coil so as to eliminate the influence from the variations in permeability.
Although detection precision for detecting a defect has been improved by former proposals, there is sometimes a failure in detecting a minute defect. In order to further improve the detection precision, it is particularly desired to prevent an eddy current probe that primarily performs flaw detection from picking up noise.
In view of these technical problems, the present invention has been made, and its object is to provide an eddy current probe that can further reduce noise presumably caused by permeability.